Some estimates of the costs and benefits of the HS2 high-speed rail line are "mumbo jumbo" calculated by men with slide rules, a former Conservative deputy prime minister has said.

Lord Heseltine said the £40bn project should be supported because it was "really imaginative" rather than fixating on its notional value for money.

He called for a greater sense of adventure about HS2 after Labour questioned its current value for money and said it would not be given a blank cheque.

Ministers are examining Heseltine's suggestion that the cost to taxpayers of Britain's first high-speed rail line north of London could be cut by up to £10bn.

The move could smooth the way for Labour to offer wholehearted support to HS2, as the transport secretary, Patrick McLoughlin, studies plans to raise extra private sector funds by selling a 30-year concession on the high-speed tracks.

Labour, which described itself last month as the "true friend" of HS2, has called on the government to bring down the costs of the line that will initially link London and Birmingham by 2026. The second phase of HS2 – Y-shaped lines to Manchester in the west and Leeds in the east – is due to be completed by 2033.

Before a speech he was due to give to the Royal Town Planning Institute on Tuesday, Heseltine said many estimates of HS2's value for money were nonsense because they left out the possibility of consequential growth.

"This is all mumbo jumbo," he told BBC Radio 4's Today programme. "The guys with slide rules, they don't know. And do you know what they leave out? There is not a single pound included for consequential growth. Now, just look at HS1 with Ebbsfleet, King's Cross and St Pancras – £10bn-worth of incidental growth has taken place."

He suggested HS2 could help restore a feeling of wellbeing in the north as the south was reaping more benefits from economic growth.

"I personally have given a lot of my time in politics trying to achieve precisely that end, trying to get a sense of adventure, a sense of expansion, a sense of can-do back into those great towns of the Midlands and the north that made this country in the first place," he said.

In his speech, Heseltine is expected to compare opponents of HS2 to critics of his regeneration of London Docklands in the 1980s.

He will endorse the call by Sir David Higgins, the incoming chairman of HS2, to reduce the overall budget by building the line more quickly.

The Tory grandee will ask: "Why does the government need to hang on to the track? We have a clear precedent. This government sold a 30-year concession in 2011 for HS1 to a Canadian pension fund for £2.1bn.

"I understand that at the same ratio, something in the order of £10bn could be realised for a similar concession on HS2. Sir David Higgins, the incoming chair of HS2, has been asked to report on how to reduce the £42.6bn cost. He should consult appropriate institutions about the financing of the project in part during construction in order to ensure their participation in the long-term concession. He should also explore the possibility of accelerating the whole project, thus offering further savings."

The concession would award a lease over the tracks, which would then earn revenue from the rail operators.

The Heseltine scheme would not bring upfront savings to taxpayers, but would lead to savings after the line had been built.

One government source said: "Patrick McLoughlin is not balking at these ideas, which are interesting. They are all about getting the project in the right place."

As well as touching on his regeneration of Docklands, Heseltine will highlight his plans to use the high-speed link to the Channel tunnel to help regenerate Stratford. "We set out to create the renaissance of east London [in the 1980s]. We faced down very similar arguments used against HS2 today.

"HS2 is about our country's competitiveness for a half-century or more. It is about so many more people sharing growth that has, for too long, been concentrated on London and the south-east. It's all about drawing together our economy as a whole as well as improving our access to the enlarged, and enlarging, home market of Europe. It is not about 30 minutes off London to Birmingham."